1. Field of the Invention
The present invention relates in general to a deflection yoke, and more particularly to an apparatus for correcting a misconvergence and geometric distortion of the deflection yoke.
2. Description of the Prior Art
FIG. 1 shows the construction of a conventional cathode ray tube (referred to hereinafter as CRT). In this drawing, the reference numeral 100 denotes the CRT and 10 denotes a deflection yoke which is mounted on a neck 110 of the CRT 100. This deflection yoke 10 is generally classified into a saddle-saddle type as shown in FIGS. 2a and 2b and a saddle-toroidal type as shown in FIGS. 3a and 3b according to the wound forms of coils. The deflection yoke 10 acts to deflect electron beams emitted from a BGR electron gun 120, installed in the neck 110 of the CRT 100, left, right, upward and downward, in order to impact them on their accurate positions of a phosphor screen of the CRT 100.
FIGS. 2a and 2b show the construction of a conventional deflection yoke of the saddle-saddle type. As shown in these drawings, horizontal deflection coils 12 of the saddle type are disposed respectively on the upper and lower portions of the inner surface of a screen part of a generally conical coil separator 11, and vertical deflection coils 13 of the saddle type are disposed respectively on the left and right portions of the outer surface of the screen part. A generally cylindrical ferrite core 14 is provided on the outer surface of the screen part of the coil separator 11 to reinforce magnetic fields of the vertical deflection coils 13. Coma precoils 15 are externally mounted on a neck part of the coil separator 11 to correct comae generated by the vertical deflection coils 13.
FIGS. 3a and 3b show the construction of a conventional deflection yoke of the saddle-toroidal type. As shown in these drawings, horizontal deflection coils 12 of the saddle type are disposed respectively on the upper and lower portions of the inner surface of a screen part of a generally conical coil separator 11, and a generally cylindrical ferrite core 14 is provided on the outer surface of the screen part. Vertical deflection coils 16 of the toroidal type are provided respectively on the upper and lower portions of the ferrite core 14. Coma precoils 15 are externally mounted on a neck part of the coil separator 11 to correct comae generated by the vertical deflection coils 16. The vertical deflection coils 16 are mechanically wound on the upper and lower portions of the ferrite core 14 and are electrically connected in series to one another in order of the left upper portion (16a-1), left lower portion (16a-2), right upper portion (16b-1) and right lower portion (16b-2) as shown in FIG. 3c.
In the deflection yoke of the saddle-saddle type as shown in FIGS. 2a and 2b, there is a difference between the left and right magnetic fields due to relative disseminations and/or relative current amounts of the left and right vertical deflection coils 13a and 13b. This magnetic field difference results in the occurrence of a misconvergence and geometric distortion (G/D) on the screen.
Similarly, in the deflection yoke of the saddle-toroidal type as shown in FIGS. 3a and 3b, there is a difference between the left and right magnetic fields due to relative disseminations and/or relative current amounts of the vertical deflection coils 16a wound on the left upper and left lower portions of X-Y coordinates and the vertical deflection coils 16b wound on the right upper and right lower portions of the X-Y coordinates. Similarly, this magnetic field difference results in the occurrence of a misconvergence and geometric distortion (G/D) on the screen.
The misconvergence is generally classified into a YV misconvergence and a YHC misconvergence. The YV misconvergence represents a vertical misconvergence where horizontal lines of red color R diverge from horizontal lines of blue color B on the upper and lower portions of the Y axis of the screen, as shown in FIGS. 4a and 4c. The YHC misconvergence represents a horizontal misconvergence where a vertical line R and a vertical line B cross each other as shown in FIG. 5. The G/D represents a distorted state on the screen as shown in FIGS. 6a and 6c. Especially, FIGS. 6a and 6c show trapezoid distortions.
FIG. 7 is a circuit diagram of a conventional circuit for correcting a YV misconvergence of the deflection yoke of the saddle-saddle type shown in FIGS. 2a and 2b. As shown in this drawing, the left and right vertical deflection coils 13a and 13b are electrically connected in series to each other. A differential shunt circuit is connected in parallel to the left and right vertical deflection coils 13a and 13b. This differential shunt circuit is provided with two fixed resistors 21a and 21b and a variable resistor 22.
In the conventional YV misconvergence correction circuit shown in FIG. 7, the relative amounts of current flowing respectively through the left and right vertical deflection coils 13a and 13b are controlled by adjusting a resistance of the variable resistor 22. As a result, the left and right relative magnetic fields are adjusted to adjust the YV misconvergence as shown in FIGS. 4a or 4c in such a manner that the R and B lines can be converged as shown in FIG. 4b.
FIG. 8 is a circuit diagram of a conventional circuit for correcting a YV misconvergence of the deflection yoke of the saddle-toroidal type shown in FIGS. 3a and 3b. As shown in this drawing, the left upper vertical deflection coil (16a-1), left lower vertical deflection coil (16a-2), right upper vertical deflection coil (16b-1) and right lower vertical deflection coil (16b-2) are sequentially connected in series. A differential shunt circuit is connected in parallel to the left upper and left lower vertical deflection coils 16a and the right upper and right lower vertical deflection coils 16b. This differential shunt circuit is provided with two fixed resistors 21a and 21b and a variable resistor 22.
In the conventional YV misconvergence correction circuit shown in FIG. 8, in a similar manner to that shown in FIG. 7, the relative amounts of current flowing respectively through the left upper and left lower vertical deflection coils 16a and the right upper and right lower vertical deflection coils 16b are controlled by adjusting a resistance of the variable resistor 22. As a result, the left and right relative magnetic fields are adjusted to adjust the YV misconvergence as shown in FIGS. 4a or 4c in such a manner that the R and B lines can be converged as shown in FIG. 4b.
However, when the YV misconvergence is corrected in the deflection yoke of the saddle-saddle type and/or saddle-toroidal type, a G/D pattern as well as a convergence pattern is varied simultaneously with the convergence pattern according to a variation in the left and right magnetic fields resulting from a variation in the relative amounts of current flowing respectively through the left vertical deflection coil 13a or 16a and the right vertical deflection coil 13b or 16b. For this reason, a new G/D occurs although the YV misconvergence has been corrected. Further, even when the variable resistor 22 is not varied, the G/D generally occurs due to a difference between disseminations of the left and right vertical deflection coils which occurs upon winding them. Namely, because of a dissemination difference resulting from a winding unbalance of the coils and mechanical assembling thereof, it is substantially very difficult that the coils wound at the first to fourth upper limits of the X-Y coordinates generate completely symmetrical magnetic fields. For this reason, due to a dissemination unbalance, the G/D may occur as shown in FIGS. 6a or 6c although the misconvergence has completely been corrected as shown in FIG. 4b. Further, the misconvergence may occur as shown in FIGS. 4a or 4c although the G/D has completely been corrected as shown in FIG. 6b. As a result, the conventional YV misconvergence correction circuits in FIGS. 7 and 8 are disadvantageous in that the misconvergence and G/D cannot simultaneously be corrected as shown in FIGS. 4b and 6b.
In the case where the deflection yoke is used for a television receiver, the G/D becomes no great issue due to a moving picture display characteristic of the television screen. As a result, the convergence is adjusted in preference to the G/D by the circuits shown in FIGS. 7 and 8. However, a precise still picture has recently been required in monitors of personal computers. This thus requires a deflection yoke capable of more precisely correcting the convergence and G/D characteristics.